1. Field of the Invention
This invention relates to an automatic stamping device which is capable of automatically imprinting desired letters or characters on documents.
2. Description of the Prior Art
Illustrated schematically in FIG. 7 is a conventional stamping device which is provided with a printing block 70 carrying a stamp unit 72 on each of stamp support surfaces 72 formed on the respective peripheral side surfaces of a triangular stamp holder 71. Each stamp unit 73 with a rectangular printing face is mounted on the stamp support surface 72 such that its longitudinal axis lies in a direction perpendicular to the axis of the stamp holder 71. In order to imprint a letter or letters on a document 74, the printing block 70 is turned about its axis until a desired stamp unit comes to a printing position on the lower side and then the printing block 70 is pressed downward with hand.
The conventional stamping device which has the rectangular stamp units 73 mounted on the holder 71 with the longitudinal axes of the respective stamp units 73 disposed in the circumferential direction of the holder, however, involves a problem that each one of the stamp support surfaces 72 of the holder is required to have, in the circumferential direction thereof, at least a length equivalent to the length of the stamp unit 73 to be mounted thereon, often resulting in a printing block 70 of an extremely large outside diameter barring provision of a compact device. For example, in case of a printing block 80 which has six stamp units 83 mounted on six stamp support surfaces 82 of a hexagonal holder 81 as shown in FIG. 8 to permit a greater variety of printing, the distance d from the center of the holder 81 to each apex needs to be at least equivalent to the length l of the stamp unit 83, and consequently the rotational diameter of the printing block as a whole including the stamp units 83 becomes more than two times as large as the length of the stamp unit 83.
Besides, the conventional stamping device requires to press down the printing block with hand when imprinting a stamp on document. Such a printing operation is troublesome, in addition to the difficulty of applying constant printing pressures on the printing block for the purpose of obtaining clean and clear impressions.